Airplane fuel system with pressure accumulator



p 1952 M. EDWARDS 2,612,215

AIRPLANE FUEL SYSTEM WITH PRESSURE ACCUMULATOR Filed Sept. 15, 1948 2SHEETSSHEET 1 E 1 4 Q L f 96 l a as 277227 Tar p 1952 M. EDWARDSAIRPLANE FUEL SYSTEM WITH PRESSURE ACCUMULATOR 2 SHEETSSHEET 2 FiledSept. 15, 1948 MZEJ" [Oh/Ell [Oh/4170f 2: 2/4,. WWW]? a 4 U a awn/ MINWm Patented Sept. 30, 1952 .UNITED STATES PATEN -[mmAIRPLANEYFUELHSYSTEM WITH PRESSURE ACCUMULATOR I Miles Lowell Edwards;Longvicw, Wash. Application September 15, 1948, Serial No. 49,320

4 Claims. (Cl. 158-363) This invention relates to a fuel pump assemblyfor an airplane fuel system and'particularly deals with an assembly forpressuring fuel flow during emergencies and under conditions ofextraordinary flight operation of the aircraft. I

In aircraftfuelsystems it is necessary to supply an ample feed of thefuel from the fuel cell or tank to the engine driven pump under allconditions and times of flight. E

To insure the aforesaid constant feed'to the engine driven fuel pump,certain difficulties must be overcome. The volatile aircraftfuel'becomes more gaseous with increases in altitude and the formationof gas or vapor bubbles is encountered. These bubbles cause theformation of airlocks I in the fuel line, interrupting the fuel supplycausing interruption in engine operation. Centrifugal type booster pumpshave been successfully employed to"beat out "these vapor bubbles at highaltitudes and topressure a constant s'up'ply 'of fuel to the enginedriven fuel pump-.-

.Another major difficulty in pressured fuel supply is encountered in themodern high-speedwartype aircraft. Such aircraft are frequently'calledupon to dive, to perform in inverted flight and to maneuver inextraordinary positions of flight, all at high speeds. During suchextraordinary flight due to the positions of the aircraft, accelerationof the aircraft or acceleration in a'dive greater than gravity forces,the fuelin a partially-filled cell maybe withdrawn from the vicinityofthe booster pumps inlet. The booster pumps are ordinarily locatedwithin the fuel cell along the bottom wall thereof. If the fuel in thepartially filled cell has collected at portions of the cell remote fromthe booster pump, due to flight operations, the booster pump cannotsupplyfuel under f pressure and again the engine willrun rough and failcompletely unless asupply of fuel-is reestablished within a short timeinterval.

Therefore, according to this invention; the

fuel cell is'equipped with a conventional booster pump adjacent itslower 'wall' and a bladder tank" or accumulator for accumulating asupply of fuel during ordinary flight and for pressuring thisaccumulated fuel to the engine driven fuel pump during the time thatfuelis not accessible to the inlet of the booster-pump. a

The bladder tank or accumulator in this invention is horizontallydisposed within the fuel'cell adjacent its lower wall and near theboosterv pump. During ordinary flight conditionsythe electric motor'driven centrifugal boosterpump pressures fuel through a line intoanupper compartment of 'the' accumulator and onward through the fuel 1line to the engine driven :fuel,

pump. An engine driven air compressor supplies air under pressure to alower compartment of the accumulator. The compartments of theaccumulator are separated by a diaphragm or bladder. The air pressure isheld constant at a figure less than the fuel pressure by a pressureregulating valve located in the air line outsideofthe fuel cell. Apressure relief valve is also located in the air line for operation ifthe air pressure should exceed a predetermined figure. A check valve islocated in the fuel line between the booster pump and the accumulator.When the booster pump cannot supply pressured fuel, as during theaforedescribed extraordinary flight conditions, the air pressure in thelower compartment of'the accumulator will expand the diaphragm orbladder forcing the accumulated fuel from the upper compartmentof theaccumulator. The fuel forced from theaccumulator by the air pressure ispressured toward'the engine-driven fuel pump because the check valvedoes -notpermit a return accelerations of the fuel toward the booster-pum'p. Under these'conditions a supply ofpressured fuel is supforsuch'extraordinary operation may be substanlator.'- 7

It is, then, an'object of thisinvention'topro- I tially predetermined bythe size of the accumuvide an improvedfuel supplysyste'm for aircraftengines whereinfuel flow to the engine is insured even during temporaryuncovering of the" fuel intake in the'tank orcellw Another object ofthis invention is to' provide 'an' aircraft booster pump unit effectivetopressure fuel under all conditions of aircraft flight and operation. II

A further object of thi'sinvention is to provide a fuel system forsupplying pressured fuel-to the engine during inverted flight of theaircraft.

Another object of this invention is toprovide a fuel system whereinaircraft engines may have a pressured supply of fuel during power divesand A specific object of. this invention is. to provide a fuelpumpingunit to supply-a pressured fuel to the aircraft engine during allmaneuvering "operations of the aircraftm;

A 'still further object of this invention is to provide an accumulatortankof such configuration and construction so as toImaintain a supply orfuel to the aircraft engine-duringall periods of extraordinary flightoperation of the aircraft.

' Other and'further objects of th e invention-will be apparent to thoseskilled; invthe artfrom the exceeding the acceleration'vof' I valvetaken as indicated by line Figure 3 is a view similar to Figure 1, but.in-i

corporating a further pressure regulating valve.

Figure 4 is a vertical cross-sectional view of the bladder tank oraccumulator.

Figure 5 is a view similar to Figure l. but. in-

corporates an additional pressure regulatingassembly.

Figure 6 is a view similar to Figure}. with a safety valve incorporatedin the fuel line.

Figure 7 is. an enlarged cross-sectional .view

- of the safety valve the fuelline of Figure 6.

Figure 8 is a horizontal sectional-viewofthe VIII-VIIIbf Figure 7. I

j 1As'shown on thedrawings: g I In'Figure 1, the reference numeral 10desig- -nates generally a pump-accumulator unit acwhic,h ;;is;-c0nnected to accumulator inlet pipe-22; .by a check valve 24.- Theaccumulator fuel inlet cording to this invention. The unit [0 is locatedwithin-a fuel cell I 2, adjacent the lower wall l4.

The unit l'll employs a- .centrifugal booster pump 16 ofconventionalconstruction which is secured to a base plate [8 on thebottom wall l4.

The booster pump l6-has a discharge line 20 line 22v is connected to theupper portion of one end-Loftheaccumulator 26-.- A fuel dischargeline..;28,isconnected to the upper portion of the op- ..posite end oftheaccumulator 26. The fuel dis- ;,,charge line 28 passes through anaperture 30 in .,a side wall 32 ofthe fuelcell l2.

marln'engine driven air compressor (not shown), supplies airunderpressure through an air inlet I ,-,pipe34 and check valve 36 to anair tank 38. An

air. outlet line connects to a pressure regulatingyalve 42;and to anaccumulator air inlet-line 44. The air inlet line 44 passes throughasealed -,.aperture,. 46;in lower wall I 4 and connects to the lower.portion of accumulator 26. A pressurerel.;lief.va1ve.44,setto dischargeat less than booster, pressure, but at a pressure greater than thedischarge pressure of valve'42, is located in the inlet 3 line, 44 tocooperate-with the pressure regulating 5.0 and aloweraqqm artm nt evalve42in maintaininga substantially constant vfairv pressure to theaccumulator 26.

The ac:- cumulator 26 is divided into anuppercompart- Asbest seenwithreference to F'gutre 4; the

accumulator 26 is of split shell-like construction.

The upper shell 54 is apertured at 56 and there has '.-boss portions 58for receiving the fuel inlet line r22. Upper shell-'54, has, afurtheraperture 60 at its opposite end and boss'portions 62 foraccommodating the fuel discharge line 28. The lower half shellportion.64 has an aperture 66 and boss portion 68 for receiving the airline 44. The upper. half shell 54 and lower half shell 64 when placedtogether form the accumulator tank26 with-the split between. the shellsbeing along the A diaphragm or bladder 14 of synthetic rubber or otherflexible'impervious sheeting isdisposed between the half shells 54 and64 with its outer periphery adjacent and between the outer periphery ofthe flanged portions 10 and 12. Suitable apertures are provided in theflanged portions 10 and 12 adjacent the outer periphery of the bladder14 so that the half shells may be secured as by the bolts I6 with thebladder 14 therebetween effectively sealing the union between the flangeportions 10 and 12.. The bladder 14 thus secured in place cooperateswith the upper half shell 54 to define the upper or fuel compartment 50and cooperates with the lower half shell 64 to define the lower or aircompartment 52 of the accumulator 26. Since the bladder 14, in operationmust necessarily be stretched to substantially conform to theconfiguration of the upper half shell 54, the humped portion 18 ofbladder 14 is designed to increase the range of flexing movement of thebladder 14.

The booster pump l6 as shown in Figure 2 has a pump casing 80 with abottom opening 82 receiving an inlet throat ring 84. Casing 80 definesthe volute chamber 86.with a peripheral outlet 86a extending through theside of the casber 86.

ing. The lower portion of the casing 80a defines a series ofperipherally spaced passages 88 through which fuel flows before reachingthe lower chamber or sump S The throat ring has a throat 90 for fuelflow into the volute cham- Adjacent and above the throat 90 animpeller92 is located which is supported by and secured to the shaft 94of an electric motor 96. The impeller 92 is rotated by the motor 96 andincludes a ring of centrifugal pumping vanes 92a.

and axial flow vanes 92b above the flow path surrounded by the vanes92a. for forcing bubble rich fuel back to the tank. The bubbles arebeaten out of the fuel and onlyfully liquid fuel is pressured into thedischarge 86a. A screen 98 extends between the casing 80 and the motor96 through which fuel must pass to reach the passage's 88 and throughwhich the beaten out gas or vapor bubbles escape. The outlet end 86a ofthe volute chamber 86 communicates with a vertical sec tion 20a of thefuel discharge line 20.

During ordinary flight operations and while the booster motor 96 isoperated, fuel is pumped by the booster pump l 6 under substantiallyconfuel section 50 to thefuel discharge line or fuel line 28 to theengine driven fuel pump.(n0t shown). During such operation the fuelcomipartment 50 'will be always filled withfuel'under sure or boosterpump pressure.

the, line on the discharge end of valve 42 at booster pump pressure. p

As previously mentioned the engine driven air compressor supplies airthrough the air line 34 and check valve 36 to the air storage tank 38from where it is discharged through the air discharge line 40, to theair pressure regulating valve 42. The valve 42 is set to discharge'theair at a maximum pressure; less than the fuel pres- When air is ingreater than this maximum discharge pressure, the valve 42 will. nolonger discharge. The air is then carried under the discharge pressureby the air line ,44 to the air compartment 52 9f the ac- ,cumulator 26.Since the air pressure is less than the fuel pressure the diaphragm 14will have a greater pressure on its upper surface 14a than it will onits lower surface 14b causing itto-bedevflected downwardly to someextent. If, due to mechanical difficulties arising in thefuel supply:or.air supply, the air (pressure should substantially increase over thepressure set by the regulator'valve 42, an upper limit to such airpressure is guaranteed by'the incorporation of the air pressure reliefvalve 48 in the fuel line '44.

The relief valve being set to operate at a pres- I sure lower thanordinary booster pressure and greater than the air pressure setting ofthe regulator valve 42. 1 1 a During periods of extraordinary flightoperations as previously described when fuel is with-- drawn from thevicinity of the booster pump I6 'so that the inlet throat 82 isuncovered. and no new supply of fuel is supplied the accumulator, theengine driven fuel pump will continue to vwithdraw fuel from theaccumulator fuel com-' partment 50. The fuel pressure within thecompartment 50 will thus be decreasedas will the ,pressure on the uppersurface 14a of the bladder 14. When the fuel pressure has reached apressure less-than the air pressure in compartment tionarymeans forpreventing the back flow of v fuel into the pump I6. Ordinarily theoperation of the booster I6, even while its inletis not submerged infuel,lwill prevent the back flow of fuel from the accumulator 26 intothe pump I6. From the foregoing it is obvious'that even during thosetemporary, periods of unusual flight where the fuel intake line isuncovered a pressured supply of fuel to the engine driven fuel pump isinsured by means of the ,boost pressure of the air in the aircompartment 52 of the accumulator 26. The air boost will maintain fuelflow until the bladder or accumulator tank is emptied of fuel and thetank can be made large enough to supply fuel during prolonged temporaryperiods. i

When recovery is made from the extraordinary flight operations and fuelagain covers the booster pump inlet, the booster pump I6 again becomesoperativein pressuringfuel to the ac cumulator. The fuel under pressurewill again displace the bladder 14 to a more normal posl-' tion and inso doing will force air from the accumulator which will be discharged bythe pressure release valve 48. A certain amount of time i necessarilyconsumed in the recovery and return to ordinary booster operations.During the time of extraordinary operation and during the recoveryperiod the booster pressure necessarily vvaries. For those enginesrequiring a more rigidly constant booster pressure, a pressure reducingvalve I00 (Fig. 3), of the type having substantially constantoutputpressure regardless of input pressure, is incorporated in the fuelline 28 outside of the fuel cell I2. In orderthat the pressure reducingor regulating valve I00 shall effectively operate to maintain a constantbooster pressure to the engine driven fuel pump during theaforementioned period, the pressure at the intake side of theregulatingvalve must be arbitrarily increased to a point above the requirement forordinary engine operation 'so'that expected variations in the pressureat the intake of valve I00 will not affect the pressure at, thedischarge side of the valve. The reducing or regulating valve- I00will-discharge the fuel atthe l I I4 which are pivoted respectively attheirlower pressure. route-air discharged from the airtank 38 through 6pressure required'by the engine. The time-interval' for recovery fromextraordinary operation will be decreased due to the increase in boosterpressure on the bladder, and the variation in booster pressure to theengine driven fuel pump would be decreased as well.

-An' alternative construction designed for an increased bladder pressureduring periods of valve I04iis.also incorporated in the air line withthexoriginal air regulating valve 42, which discharges at apressure'less thanbooster pressure,

but the valve I04 is set to discharge air at a pressurelequal to orslightly above booster pumpfuel The airvalve, I02 is constructed to the:original 'air regulating valve 42 to the accumulator 26 during normalbooster pump opera-- tion-and topass air through the higher 'setairregulating valve I04 to bypass valve during periods of booster pumpinoperation. The foreline 20 between'the check valve 24 and the .boosterpump I6 andpassing the tapped fuel to abellows I08located;withinthe airvalve I02.

The bellows I03. is responsive to the booster pump fuel pressureformovement and operates a spring loaded to gle-plate I I0 which ispivoted about a pivot pin IIIla. A toggle linkage H0!) is connected to apair of valve plug arms II2 and extremities by the pivot pins II2a andH411. The valv plug I I4 is located within an air sealed container II6for closing or opening thedischargeyline IIl4a of'the high pressureregulator valve I04. The valve plug II2 is positionedfor closing oropening thedischarge line 48a of the air relief-valve 48. During normalbooster pump operations the booster pump fuelpressure expandsthe bellowsI08 activating the toggle plate H0 and its linkages IIIlb so that thevalve plug II2 is unseated fromthe relief valve discharge line 48a andso that the valve plug I I4 is seated and closing the high pressureregulator discharge vline I04a. In such a position the air from the airtank 30 passes through the original air regu-' lator valve 42, bypassingregulator I04 and on into the accumulator 26 inthe regular manner.

However, during periods of booster pump inoperation and the consequentlowering of the booster pump fuel pressure in the bellows I08, themovement of the toggle plate III] is in a counterclockwise manner (Fig.5 The air pressure relief discharge line-40a is closedbythe valve plugII2 and the valve plug I I4 unseated from the high pressure dischargeline I04a.. In such a-position, the air passing from the air tank 38 isrouted through the high pressure air regulator valve I04 into dischargeline I04a into the air container ,I I6 under the higher pressure anddischarged from the container II6 into, the ex-' tension 44a ofthe airline 44 and on to the accumulator 2 6.

From the foregoing, it can readily be seen that during periods ofbooster pump inoperation and due to-the toggle action of the air valveI02, the air pressure in the accumulator 26 increases to-a the-line 28.When the booster pump I B-comes back into operation a shift within theair valve I02 Occurs in the opposite direction andithe air pressurewithin the accumulator is immediately .reduce'd to aid in the. quickrecovery to normal operation of the fuel system.

- For the War type. aircraft Where battle damage must be foreseen orexpected; provisions mustbe made for continuous pressured fuel supply.inithe event of damage or inoperation of the bladder or accumulatortank. With reference to Figured, a special safety or check valve H8 hasbeen incorporated in the booster fuel line 22 between the check valve 24and the accumulator 26. The construction of the unit I is varied so thatthe fuel discharge line 28 is not connected directly to the accumulator26 but communicates with the booster fuel line 22 at the same end of thespecial valve H8. It is obvious that in such a construction thesafety'valve I I8 must allow -the passage of fuel into'theaccumulator26during normal operation until the fuel compartment 50 isfilled with fuel at booster pressure. Thereafter fuel from the boosterpump I6 passes directly to the engine driven fuel line 28. The safetyvalve II8 mustalso allow for. the passage of fuel under air pressurefrom the accumulator '26 into the engine driven fuel line 28 duringperiods when the booster pump is inoperative.

The safety valve IIB must also provide for the stopping of fuel flowfrom the line 22 into the accumulator 26 when the bladder or accumulatortank 26 is damaged or due to some other cause loses pressure.

The construction of safety valve H8 to fulfill the foregoingrequirements may be best understood in view of Figure'l. The valve H8comprises an upper casing II8a and a lower casing =I I81) of smallerdiameter than the upper casing stem guides II8cZ and HM have centralapertures therethrough for accommodating the valve stem By. The lowerextremity of the valve stem I I8g is threaded'to accommodate theadjusting nut Ni and has a central boss portion II8i upon which thevalve gate H87 rests. A.

coil spring I I8k is disposed about the valve stem H89! between theupper valve stem guide II8d and the valve gate I I87. A lower coilspring I I 8p is disposed between the central boss'portion II8i on thevalve stem I I89 and the lower valve stem guide H8 The spring II8p has arelatively higher compressive force than the spring II8k 'and as aconsequence thereof the vertical position of the valve gate H8 1 may beadjusted by positioning the adjusting nut II8h on the valve stem IIBg.As shown in Figure 7 the gate 87' is adjusted to provide a gap IISmbetween the gate and the valve seat II8n, when-fuel under accumulatorfuel pressure is present on the un derside of the gate. If fuel pressurewithin the accumulator is withdrawn as by damage to the accumulator, thefuel under booster pump pressure in the booster fuel line 22 will enterinto the safety valve intake duct I20 and on 'into the cavity of theupper casing II8a. Here the '-fuel will close the valve gateIlaja'gainst the valve seat- M with a; snap due to its pressureand dueto the lack of pressure on the underside of the valve gate H87. Duringbooster operation, however, and while 'therejis' fuel pressure presentin the accumulator 26, the accumulator fuel pressure aided by thepressure of the spring II-Bp will keep the valve gate H81 away from theseat II8n allowing for the gap II8m which is shown inthe figure.

During periods of booster pump failure due to extraordinaryflightconditions, accumulator fuel pressure on the 'under sldeof thegate H8 will cause a wider gap and the fuel will leave the'accumulatorin the aforedescribed manner through the 'duct I28. and into the fuelline 28 to theengine driven fuel pump.

Accumulator fuel pressure may be greatly decreased or non-existent durinthe periods of time when the aircraft engine is idling and when thebooster pump I6 is not operating. During recovery from such periods thevalve gate I'I87' may be closed. It is desirable that fuel be allowed toenter the accumulator through the safety valve discharge duct I22 andthis is accomplished by placing a small hole or aperture I24 in'thevalve gate H87 so that fuel under pressure may be slowly returned to theaccumulator. When thefuel compartment 50 of the accumulator 26 has beenfilled with fuel under booster pump :pressure the gate IIByTwill againbe vertically displaced under the .force of spring I lap and accumulatorfuel pressure.

It will be understood from the foregoing that with the incorporationofthe safety-valve II8 that the accumulator and'air-pressure units can becompletely inoperative and that the booster pump I6 can be completelyinoperative without stopping the flow of fuel from the fuel cell to thefuel line 28, since the fuel can always flow through the impellerand'cas'ing of the pump, whenever there is asuction pull in the fuelline,

' as when the engine driven fuelpumpis operative and the booster pumpmotor unit is inoperative. i" I-.

It will, of course, also be understood that various details ofconstruction may be varied through a wide range without departing "fromthe principles of this invention and it is, therefore, not the purposeto limit the patent granted hereon otherwise than necessitated -.by thescope of the appended claims. l

:I claim as my invention: In an aircraft fuel system, a fuel cell, apump having an inlet receiving fuel from said fuel cell and a dischargeconnected to a supply line,

- a tank connected to'said line through a check valve, said check valveclosing upon a differential of pressure in said line overthat insaidtank, means permitting a small flow of fuel from said line to said tank,and means for applying pressure to fuel in said tank.

2. In an'aircraft fuel'system, a fuel cell, a pump having an inletreceiving fuel from said fuel cell and a discharge connected to a linefor supplying' fuel to the aircraft engine,a tank connected to sa1d linthrough a check valve, said check valve comprising a gate urged to openposition and operated to closed position .bya differential ofpressure insaid line overthat in said tank. sa1d gate having an opening'permittinga small I flow of fuel from said line to said tank; and meansfor'applying pressure to fuel in said tank.

3.1 A fuel system for aircraft or the like which comprises a fuelcell, abooster'pumip for pressuring fuel from said cell, a discharge conduitferential of pressure in said conduit over that in said tank.

4. A fuel system for aircraft or the like which comprises a fuel cell, abooster pump for pressuring fuel from said cell, a discharge conduitreceiving pressured fuel from the booster pump, an accumulator tankhaving a fuel compartment and a gas compartment separated by a flexibleimpervious wall, means connecting the discharge conduit with the fuelcompartment of the tank, means for pressuring the gas compartment ofsaid tank so as to displace said flexible wall and pressure fuel fromsaid tank during inoperation of said booster pump, a safety valveinterposed between said discharge conduit and said fuel compartment ofsaid tank, a valve grate resiliently urged to open position and closedby a differential of pressure in said discharge conduit over that insaid tank.

MILES LOWELL EDWARDS.

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